| Summary: | 碩士 === 國立臺灣海洋大學 === 環境生物與漁業科學學系 === 100 === Abstract
In this study, fishery indicators, including weigh frequency, central trend, maximum weight, the proportion of mature catch, catch frequency and mean catch per trip, were used to analyze the trend of population status for five billfishes caught in the waters off eastern Taiwan.
For black marlin and sailfish, the results of this study indicated that the size indicators showed a relatively stable or increasing trend, the proportion of mature catch was high, mean catch per trip also gradually increased. Therefore, fishing exploitation might not lead to the decreases in the body size and the mature proportion for black marlin and sailfish in the waters off eastern Taiwan. Although size indicators and the proportion of mature catch of striped marlin increased in recent years, the catch frequency and mean catch per trip revealed obvious decreasing trend. Therefore, the population status of striped marlin in the waters off eastern Taiwan is needed to be further monitored. In recent years, size indicators of blue marlin and swordfish gradually decreased and the proportion of mature catch was also under relatively low level. Although the mean catch per trip and catch frequency slightly increased in recent years, most of indicators indicated that fishing exploitation might have led to the decreases in the body size and the mature proportion for blue marlin and swordfish in the waters off eastern Taiwan.
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